The vitreous body is a clear, transparent gelatinous substance in the vitreous cavity of the eye that is posterior to the lens and anterior to the retina. It occupies two thirds of the ocular volume; with a weight of approximately 4 g and a volume of about 4 ml. The main components of vitreous body include water (98%), collagen fibrils, glycosaminoglycans, hyaluronic acid (HA) and other rest solutes. Specific diseases, age-related degeneration or trauma can lead to pathological changes in the vitreous body, including HA degeneration and collagen precipitation, which result in liquefaction of the matrix. A degenerated or liquefied vitreous body will lead to floater formation and eventually result in posterior vitreous detachment and possible retinal detachment.
Among clinical treatments, pars plana vitrectomy (PPV) is one of the most important surgeries for treating a number of ocular-related diseases, including diabetic retinopathy, complex retinal detachment (for example, due to trauma) and macular hole. During PPV, the vitreous body is cut and aspirated, and then is typically replaced with a vitreous substitute, such as gas (air, perfluoropropane or sulfur hexafluoride) or silicone oil. Vitreous substitutes are used to fill vitreous cavity and help reattach the retina after vitrectomy surgery. Postoperatively, a vitreous substitute can keep the retina in position while the adhesion between the retina and the retinal pigment epithelium (RPE) cells forms. Gases, which are lighter than water, are useful for flattening a detached retina and keeping it attached while healing occurs. However, it is frequently necessary to maintain a face-down position following surgery for a week or more when gas is used. Silicone oil is sometimes used instead of gases to keep retina attached postoperatively since 1960s for complicated retinal detachments, or in patients unable to position postoperatively (e.g. children), but long-term complications can occur if the silicone oil is not removed later. Besides, silicone oil also may be cytotoxic to ocular tissues, such as corneal endothelial cells.
Recently, numerous vitreous substitute materials using natural, semi-synthetic or synthetic polymer have been investigated, including poly(vinyl alcohol), poly(1-vinyl-2-pyrrolidone), poly(acrylamide), poly(glyceryl methacrylate), poly(methyl-2-acrylamido-2-methoxyacetate) and poly(2-hydroxyethylacrylate). Criteria for the ideal vitreous substitute include clarity, transparency, refractive index, sufficient rigidity to act as a tamponade substitute, ability to allow metabolite transfer, non-absorbable characteristics, hydrophilic composition and the ability to be injected through a small-gauge needle. These criteria suggest that finding a proper material for a vitreous substitute is not an easy task.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies, especially in connection with vitreous substitutes.